The invention relates to a brake cylinder for pneumatically actuated vehicle brakes, in particular for commercial vehicles.
In heavy commercial vehicles, the parking brake is actuated by what are known as spring force accumulator cylinders (spring-loaded cylinders). Here, the brake actuating force is generated via spring force, with the result that the requirements for a mechanically actuated parking brake are satisfied.
Since the spring force accumulator cylinders are, as a rule, designed to generate very high forces, manual release in the operating case is no longer appropriate. In the case of pneumatically actuated brakes, the parking brake is therefore released by means of compressed air.
In order to make this possible, spring force accumulator cylinders are, as a rule, equipped with a release piston. It is possible by way of this piston, if compressed air is introduced, to compress the spring to such an extent that the brake is released. In order that the parking brake is not engaged while driving, the piston is loaded constantly with compressed air, with the result that the spring cannot be relieved and therefore the parking brake does not start to act.
The most common design is what is known as a combined cylinder. A combined cylinder includes or combines two different brake cylinder types, namely a spring force accumulator cylinder for the parking brake system (PBS) and a compressed air cylinder (usually a diaphragm cylinder) for the service brake system (SBS).
The two cylinders are usually arranged behind one another in an axial direction. The spring force accumulator part, which acts with its piston rod on the piston collar of the diaphragm cylinder and by the latter, in turn, on the brake lever, is arranged behind the diaphragm part of the combined cylinder.
This design requires a relatively large amount of installation space. However, the installation space is being limited increasingly by the introduction of more complex chassis systems, such as independent suspension systems, lightweight axles, etc.
There are therefore efforts to minimize the space requirement for the parking brake cylinder by other designs and methods of operation. To this extent, what is known as a compact combined cylinder affords a more compact design. DE 10 2005 044 708 A1 (corresponding to U.S. Pat. No. 7,523,999 B2) discloses a brake cylinder of this type, in which the function of the parking brake cylinder is integrated directly into the service brake cylinder. Here, the spring force accumulator spring is no longer actuated via a separate spring force accumulator piston, but rather likewise via the piston of the service brake cylinder. In order to release the parking brake, the SBS piston is loaded for a short time period by way of a special actuation with compressed air. Since the piston force which is produced here is greater than the maximum compressive force of the accumulator spring, the latter is compressed. Subsequently, the spring is arrested by way of a pneumatically actuated locking mechanism, and subsequently the cylinder piston is ventilated. The cylinder piston can then be moved with the compressed and arrested accumulator spring into the rest position by the piston restoring spring.
The parking brake is engaged by the ventilation of the pneumatically actuable locking mechanism of the spring force accumulator spring. The locking mechanism realizes a very important functional unit for the overall function of the compact combined cylinder. High requirements are therefore made of the functional response and the reliability of this component.
The mechanism can be realized in different ways. One possibility includes arresting the spring via a threaded spindle, which is not self-locking. To this end, it is required to arrest the threaded spindle by a pneumatically switchable clamping mechanism or locking mechanism.
It is therefore the object of the invention to provide a brake cylinder of the generic type with a clamping mechanism, which is functionally reliable and can nevertheless be realized with manageable structural expenditure.
The invention achieves this object by a brake cylinder for pneumatically actuated vehicle brakes, in particular for commercial vehicles, having a spring force accumulator brake section for carrying out parking brake operations by way of a spring force accumulator spring, and a service brake section for carrying out service brake operations, which are actuated by compressed air. The spring force accumulator brake section and the service brake section are combined in a housing to form one structural unit. The housing is divided by a piston into two spaces, of which one of the two spaces serves as pressure space for actuating the service brake section. The spring force accumulator spring of the spring force accumulator section is arranged in the further space on the opposite side of the piston. The spring force accumulator spring acts in the space on a further spring force accumulator piston, which can be locked with respect to the piston by way of a pneumatically actuable locking mechanism and can be released from the locking mechanism by release of the latter, and which is connected directly or via further elements to a piston rod for actuating the vehicle brake. After the release of the locking mechanism, the spring force accumulator spring acts between the two pistons and displaces them relative to one another in the case of a parking brake operation. The locking mechanism is designed as a pneumatically actuable clutch.
Advantageous refinements of the invention are described herein.
In order to arrest or to release the threaded spindle, the pneumatically actuated clutch is advantageous. In clutches, there are in principle two different action principles, firstly what are known as the friction clutches and secondly what are known as the claw clutches. Both variants are used.
The invention realizes a brake cylinder having a clamping mechanism which is of simple construction, can be produced simply and affords a reliable clamping action in all possible operating conditions. To be highlighted here are firstly the high immunity to vibrations, the satisfactory and reproducible release behavior, the high fatigue resistance and the high wear resistance, and secondly the small installation space requirement of the construction.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of one or more preferred embodiments when considered in conjunction with the accompanying drawings.